Blockage detection in millimeter wave radio communications

ABSTRACT

Blockage detection in a wireless transmit receive unit includes performing a radio link measurement on one or more reference signals. The radio link measurement is compared to a comparing threshold and a blockage condition is indicated in response to the comparing of the radio link measurement meeting a threshold criterion on the comparing threshold.

RELATED APPLICATION DATA

This application claims priority under 35 U.S.C. § 119(e) from U.S.Provisional Patent Application No. 62/449,687 entitled “Method ofMulti-Radio Control for TCP Throughput Enhancement,” filed Jan. 24,2017, the entire disclosure of which is incorporated herein byreference.

BACKGROUND

Millimeter wave radio communications (corresponding to radio frequenciesabove roughly 10 GHz) afford substantially higher data capacity thantheir longer wavelength counterparts. Consequently, communications atsuch frequencies are one of the central enhancements being adopted inthe 3^(rd) generation partnership project (3GPP) standards for the nextgeneration, so-called 5G, mobile telecommunication networks. While 5Gwill provide data rates in the 10 Mbit/s-1 Gbit/s range, shorterwavelength radio communications suffer high variability in radio linkquality. Indeed, buildings, automobiles and even the human body caninterfere with millimeter wave radio, thus diminishing the quality ofthe affected radio links.

FIG. 9 depicts a blocker 10 being interposed between user equipment (UE)110 (also referred to as a wireless transmit and receive unit (WTRU))and a transmitter (not illustrated). As illustrated in the figure,blocker 10 has a dimension W that is transverse to the directionality ofthe UE antenna, is located a distance D from UE 20 and is moving atvelocity V. Table 30 illustrates radio link outage intervals fordifferent types of blockers 10, where items 32 may correspond to a largetruck, items 34 may correspond to a passenger automobile and item 36 maycorrespond to a human body. As FIG. 9 demonstrates, considerable radiolink outage may occur in the presence of these blockers.

FIG. 10 illustrates another blockage scenario in which passengerautomobiles 12 a-12 d, representatively referred to herein asautomobile(s) 12, are moving at a velocity V and maintaining a distanceD_safe between one automobile 12 to the next. In such a case, theblockage is intermittent, with the time between successive blockageevents being illustrated in Table 40.

While physical layer interference is entirely expected in the presenceof blockers, what is less expected is the dramatic effect on thetransport layer that such blockage entails. FIG. 11 illustrates theeffect on data rate 50 and TCP sender window size (MSS per the TransportControl Protocol (TCP)) 60 responsive to blockage at blocking intervals55 a-55 e, representatively referred to herein as blocking interval(s)55. As illustrated in the figure, there is significant degradation indata throughput in the presence of blockers, but such degradation isattributable not just by a drop in radio signal strength or quality.Indeed, radio blockage has a profound impact on data transport such asby TCP as demonstrated by Table 1 below.

TABLE 1 Blockage TCP Blockage Model Ratio TCP Throughput Degradation NoBlocking 0% 807 Mbps 0% 0.1 s blocking every 5 s 2% 712 Mbps −12% 0.2 sblocking every 5 s 4% 371 Mbps −54% 1 s blocking every 5 s 20% 229 Mbps−72%

The causes of such dramatic drop in TCP throughput over thecorresponding blockage ratio include TCP sender retransmission timeout(RTO) and congestion control mechanisms was triggered such as windowshrinking. Overcoming such degradation in TCP throughput is a subject ofongoing research and engineering efforts.

SUMMARY

Blockage detection in a wireless transmit receive unit includesperforming a radio link measurement on one or more reference signals.The radio link measurement is compared to a comparing threshold and ablockage condition is indicated in response to the comparing of theradio link measurement meeting a threshold criterion on the comparingthreshold.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is a schematic block diagram of an example system in which thepresent general inventive concept can be embodied.

FIG. 2 is a schematic block diagram of an example dual connectivity modein which embodiments of the present general inventive concept can beconfigured.

FIG. 3 is a block diagram of example logic flow in accordance with whichthe present general inventive concept can be embodied.

FIG. 4 is a flow diagram of an example blockage detection process bywhich the present general inventive concept can be embodied.

FIGS. 5A-5B are graphs representing different blockage indications thatcan be used in conjunction with embodiments of the present generalinventive concept.

FIG. 6 is a flow diagram of an example uplink bearer switching processby which the present general inventive concept can be embodied.

FIG. 7 is a flow diagram of an example downlink bearer switching processby which the present general inventive concept can be embodied.

FIG. 8 is a flow diagram of an example TCP enhancement process by whichthe present general inventive concept can be embodied.

FIG. 9 is a diagram of a millimeter wave radio blockage scenario.

FIG. 10 is a diagram of another millimeter wave radio blockage scenario.

FIG. 11 is a set of graphs illustrating the impact of millimeter waveradio blockage on TCP throughput.

DESCRIPTION

The present inventive concept is best described through certainembodiments thereof, which are described in detail herein with referenceto the accompanying drawings, wherein like reference numerals refer tolike features throughout. It is to be understood that the terminvention, when used herein, is intended to connote the inventiveconcept underlying the embodiments described below and not merely theembodiments themselves. It is to be understood further that the generalinventive concept is not limited to the illustrative embodimentsdescribed below and the following descriptions should be read in suchlight.

Additionally, the word exemplary is used herein to mean, “serving as anexample, instance or illustration.” Any embodiment of construction,process, design, technique, etc., designated herein as exemplary is notnecessarily to be construed as preferred or advantageous over other suchembodiments. Particular quality or fitness of the examples indicatedherein as exemplary is neither intended nor should be inferred.

Embodiments of the invention ameliorate deteriorative effects onconnection-oriented application layer data transport, such as thetransmission control protocol (TCP), in the presence radio signalblockage. While the embodiments described herein are directed tomitigating TCP issues in a 5G next generation or “new” radio (NR)embodiments, such is solely for purposes of description and explanation.Those having skill in the art will recognize other network environmentsin which the present invention can be realized without departing fromthe spirit and intended scope thereof.

For purposes of succinctness and clarity, suitable shorthand notationwill be adopted to indicate a distinction between radio accesstechnologies. While 5G can be considered a progression of the long termevolution (LTE) standards maintained by 3GPP, the acronym LTE will beused herein to refer to legacy LTE evolved universal mobiletelecommunications system (UMTS) terrestrial radio access (E-UTRA)implementations, e.g., 4G, while the acronym 5G will refer toimplementations that include NR operating at millimeter wavelengths.

FIG. 1 is a schematic block diagram of an example system 100 by whichthe present invention can be embodied. UE 110 may be a wireless transmitand receive unit (WTRU) comprising radio circuitry 110 a, processorcircuitry 110 b and memory circuitry 110 c. UE 110 may be constructed orotherwise configured to communicate with an LTE evolved Node B (eNB) andwith a 5G next generation node B (gNB) comprising radio circuitry 120 aand 130 a, respectively, processor circuitry 120 b and 130 b,respectively and memory circuitry 120 c and 130 c, respectively. UE 110may be communicatively coupled to eNB 120 over a signaling link 152 andto a gNB 130 over a signaling link 154. ENB 120 and gNB 130 may becommunicatively coupled to a core network, such as the LTE evolvedpacket core (EPC) 140, over signaling links 156 and 158, respectively.Additionally, eNB 120 and gNB 130 may be communicatively coupled to eachother over suitable signaling link 155. Those having skill in the artwill appreciate that, although not illustrated in the figure, signalinglinks 152, 154, 155, 156 and 158 may carry either or both control planedata and user plane data, depending on the connected entities. Theskilled artisan will recognize that environment 100 represents a 5Gnon-standalone (NSA) architecture implementation.

Resources in eNB 120 and gNB 130, e.g., radio circuitry 120 a and 130 a,processor circuitry 120 b and 130 b and memory circuitry 120 c and 130c, may be constructed or otherwise configured to realize radio protocolstacks 125 and 135, respectively. Each radio stack 125 and 135 mayrealize, among others, a radio resource control (RRC) layer, a packetdata convergence protocol (PDCP) layer, a radio link control (RLC)layer, a medium access control (MAC) layer and a physical (PHY) layer.The RRC layers, PDCP layers, RLC layers and MAC layers are specificallyconfigured for the radio access technology, LTE or NR, utilized at thatparticular radio node. Resources in UE 110, e.g., radio circuitry 110 a,processor circuitry 110 b and memory circuitry 110 c, may be constructedor otherwise configured to realize radio protocol stacks 115 a and 115b, each comprising an RRC layer, a PDCP layer, an RLC layer, a MAC layerand a PHY layer. Radio protocol stacks 115 a and 115 b are constructedor otherwise configured for each radio access technology utilized in eNB120 and gNB 130, e.g., LTE and NR, respectively.

FIG. 2 illustrates a dual connectivity configuration 200 that may beused in conjunction with embodiments of the present invention. In dualconnectivity configuration 200, 5G NR PDCP entities may becommunicatively coupled to LTE E-UTRA RLC entities. While such couplingtakes place onboard UE 110, the communication between eNB 120, servingas master node MN, and gNB 130, serving as secondary node SN, mayproceed over the X2 interface. Dual connectivity configuration 200allows UE 110 to simultaneously transmit and receive data on multiplecomponent carriers from two cell groups via master node MN and secondarynode SN. This is a distinction from carrier aggregation (CA) whichallows UE 110 to simultaneously transmit and receive data on multiplecomponent carriers from a single base node. CA traffic is split in theMAC layer, while E-UTRAN dual connectivity (EN-DC) is split in the PDCPlayer.

In the system configuration of FIG. 1, UE 110 is configured to conveydata over alternate links, either through two separate PDCP entitiescorresponding to individual bearers or a single PDCP entitycorresponding to a split bearer. In certain embodiments, traffic istransported over a first bearer between UE 110 and, for example, gNB 130until the link quality meets some unacceptability criterion, such as anindication of blockage. Responsive to the link quality meeting theunacceptability criterion, traffic may be transferred to an alternativebearer between UE 110 and, for example, eNB 120.

FIG. 3 is a flow diagram of an exemplary embodiment of the presentinvention comprising blockage detection logic 310, by which diminishedradio link quality situations are identified, bearer switching logic320, by which radio link quality issues are mitigated and TCPenhancement logic 330, by which TCP operation is restored once suchradio link quality mitigation has occurred. It is to be understood thatwhile blockage detection logic 310, bearer switching logic 320 and TCPenhancement logic 330 are illustrated in FIG. 3 as contained in acomposite flow, each of these components may be used alone in othercontexts, as the skilled artisan will appreciate upon review of thisdisclosure.

FIG. 4 is an exemplary blockage detection process 400 that may beimplemented by blockage detection logic 310. In operation 405, radiolink characteristics of NR are monitored. Blockage detection logic 310may continuously perform radio link monitoring to determine when radioblockage is occurring. Such may be achieved by various mechanismsonboard UE 110, e.g., conventional measurements configured by the RRClayer and radio link monitoring performed by the Physical layer.

In operation 410, it is determined whether there are characteristics ofblockage in the measured radio characteristics. In certain embodimentsof the invention, UE 110 may monitor one of several different parametersof the radio link to determine whether blockage is occurring, includingreference signal received power (RSRP), reference signal receivedquality (RSRQ), received signal strength indicator (RSSI), signal tointerference plus noise (SINR), block error rate (BLER) and channelquality indicator (CQI). Such parameters may be compared with respectivethresholds established by a user or network administrator. In otherimplementations, blockage may be identified from increasing latency ofacknowledgments of RLC PDUs, increasing queuing time in layer 2 bufferand degradation in successful delivery indication as HARQ ACK.

Referring to FIG. 5A, there is illustrated a graph that demonstratesin-sync and out-of-sync conditions according to one embodiment, whereselected number of out-of-sync indications provides evidence of radiolink blockage. Here, a serving beam and candidate beam are compared to ablock error rate (BLER) threshold that determines whether each beam isin-sync or out-of-sync. The BLER may be compared with a suitablethreshold, e.g., LTE defines a threshold of 2% (Qin) on the PDCCH blockerror rate as in-sync and 10% (Qout) as out-of-sync.

FIG. 5B is another graph depicting how a beam may be identified asblocked. In this case, historical data are maintained and whether a beamis blocked is determined by whether the quality of that beam hasdecreased by an amount determined from the historical data. Variousstatistics may be derived from the historical data that can be used toestablish an unacceptability criterion, such as a radio qualitythreshold. For example, Threshold 1 may be a difference between acurrent radio link measurement on a serving beam and a historical radiolink measurement and Threshold 2 may be a difference between a currentradio link measurement on a candidate beam and the historical radio linkmeasurement.

Returning to FIG. 4, if it is determined at operation 410 that there arecharacteristics of blockage present, process 400 may transition tooperation 420, by which it is determined whether a blockage report is tobe issued by UE 110. In certain embodiments, a blockage report is asuitably formatted message that indicates to network entities that ablockage condition (such as determined per the unacceptability criteriondescribed above) exists. Such message may contain information relevantto radio resource management, such as measurement result and beaminformation. The radio resource manager may utilize the information totake some action, e.g., select a different beam or assert anotherscheduling policy. In certain implementations, a blockage report may notbe necessary, in which case the sending of the report can be omitted. Ifa report is to be issued by UE 110, as determined in operation 420,embodiments of the invention may format and convey a blockage reportindicating such to the network in operation 425. The blockage report canbe sent via a newly active uplink, such as described below.

Responsive to blockage being detected, embodiments of the invention mayperform bearer switching from an NR bearer to an LTE bearer. Two modesof bearer switching are contemplated for embodiments of the invention:an autonomous mode in which the uplink is switched from NR to LTEwithout a prior report being sent and a network assisted mode in whichthe uplink is switched only after the network has approved the switch inresponse to a blockage or other report. For example, in certainembodiments, UE 110 may format and send an RRC measurement report to EPC140, in response to which EPC 140 may initiate an RRC connectionreconfiguration procedure with UE 110. In the autonomous switching mode,UE 110 does not require an RRC message to command the switching,instead, the UE itself selects the UL transmission path among the twocell groups.

FIG. 6 is a flow diagram of an exemplary bearer switching process 600that may be implemented by bearer switching logic 320. In operation 605,UE 110 determines of selects an active uplink cell group. For example,UE 110 may select NR link as active cell group with gNB 130. Uplinktraffic is conveyed over the active link in operation 610, where the LTEradio is utilized as a backup radio in the event of blockage. In certainembodiments, when UE 110 is not in active transmission mode with any oneof the cell groups, the associated radio circuitry can be placed in areduced power mode.

In operation 615, it is determined whether an uplink switch is required.Such uplink switching may be required when a blockage condition exists,but the invention is not so limited. If uplink switching is required,process 600 may transition to operation 620, by which transmissionsbetween UE 110 and the active cell group are suspended. In operation625, UE 110 switches to or otherwise selects an alternative cell group,e.g., eNB 120. Once this has been achieved, radio link monitoring maycontinue in order to determine when the blocking condition (or otherunacceptable condition) is lifted.

In operation 630, missing PDUs are restored. During the latency periodbetween when the radio link quality fails and when the radio switchingoccurs, some packets may be lost. In one embodiment, the PDCP layershall guarantee that data for which an acknowledgment has not beenreceived is retransmitted. In certain embodiments, upon UE 110 switchingthe radio link, UE 110 shall ensure the data sent but unacknowledged inthe previous link are retransmitted in the new link responsive to arequest for such from EPC 140. In other embodiments, a report may beformatted and conveyed so that missing blocks can be retransmitted overLTE. This may be achieved by a suitably formatted PDCP status report.

Certain embodiments implement a rapid recovery mechanism employed whenit is determined that blockage has been lifted and system 100 is torecover. For example, when there are characteristics of blockagepresent, the original UL configuration is cached under a resumptiveconfiguration ID for rapid re-establishment of NR operations once theblockage ceases. In certain embodiments, this may be achieved byrequesting relevant information, e.g., cell ID, band configuration,etc., from the network via eNB 120. Upon recovery, both the network andthe UE 110 can recall its configuration from memory by the resumptiveconfiguration ID. UE 110 may switch traffic to its NR in recovering froma previous switch according to the configuration data stored under theresumptive configuration ID.

FIG. 7 is a flow diagram of an example downlink bearer switching process700. In operation 705, UE 110 receives its initial configuration toselect a link in an active downlink cell group. For example, UE 110 mayestablish a link with gNB 130. In operation 710, it is determinedwhether downlink switching is required, such as in the case of blockage.If downlink switching is required, process 700 may transition tooperation 715, by which downlink transmissions between UE 110 and theactive cell group are suspended. In operation 717, UE 110 switch thetransmissions with the active cell group into reduced power mode. Inoperation 720, UE 110 switches to or otherwise selects an alternate cellgroup, e.g., eNB 120. In operation 723, the alternate cell is awokenfrom its reduced power mode.

Once a quality radio link has been established over LTE, embodiments ofthe invention may turn to mitigating TCP flow and congestion controlissues created when the NR radio link failed. FIG. 8 is a flow diagramof an exemplary TCP enhancement process 800 that may be implemented inTCP enhancement logic 330. In operation 805, it is determined whetherTCP ACK reduction is required, such as to conserve radio resources. Ifso, process 800 may transition to operation 810, by which TCP ACKs arefiltered to remove those that can be omitted and replaced by a singleACK with the suitably encompassing sequence number. Additionally, asillustrated in FIG. 8, embodiments of the invention may determinewhether there is deterioration in TCP throughput, such as by monitoringflows in the active link. If so, process 800 may transition to operation820, whereby UE 110 may send an upstream DSACK to return the window toits original state.

The descriptions above are intended to illustrate possibleimplementations of the present inventive concept and are notrestrictive. Many variations, modifications and alternatives will becomeapparent to the skilled artisan upon review of this disclosure. Forexample, components equivalent to those shown and described may besubstituted therefor, elements and methods individually described may becombined, and elements described as discrete may be distributed acrossmany components. The scope of the invention should therefore bedetermined not with reference to the description above, but withreference to the appended claims, along with their full range ofequivalents.

The invention claimed is:
 1. A method of blockage detection in awireless transmit receive unit (WTRU), the method comprising: performinga radio link measurement on one or more reference signals; comparing theradio link measurement to a comparing threshold; indicating a blockagecondition in response to the comparing of the radio link measurementmeeting a threshold criterion on the comparing threshold; sending ablockage report to a network core in response to the comparing of theradio link measurement meeting the threshold criterion; starting a timerwhen a first blockage condition is satisfied; and determining theblockage if the blockage condition is still satisfied after timerexpiry.
 2. The method of claim 1, wherein the reference signals areassociated to a serving beam or a candidate beam.
 3. The method of claim1, wherein the comparing threshold is determined by a latest radio linkmeasurement and a historical radio link measurement.
 4. The method ofclaim 1, wherein the comparing threshold is configured at a networkcore.
 5. The method of claim 1, wherein the radio link measurement is tomeasure one or more of the group comprising reference signal receivedpower (RSRP), reference signal received quality (RSRQ), received signalstrength indicator (RSSI), signal to interference plus noise (SINR),block error rate (BLER) and channel quality indicator (CQI).
 6. Themethod of claim 1 wherein the blockage condition is met when either theradio link measurement is above the comparing threshold or the radiolink measurement is above the comparing threshold for a predeterminedtime period.
 7. The method of claim 6, wherein the time period iscontrolled by a timer or a counter, and the values are configured at anetwork core.
 8. The method of claim 1, further comprising selecting thetransmission path in which to send the blockage report from dualconnectivity or carrier aggregation.
 9. An apparatus comprising: radiocircuitry by which wireless electromagnetic radio signals are conveyedto and from one or more radio nodes; and processor circuitry configuredto: perform a radio link measurement on one or more reference signals;compare the radio link measurement to a comparing threshold; indicatinga blockage condition in response to the comparing of the radio linkmeasurement meeting a threshold criterion; start a timer when a firstblockage condition is satisfied; and determine the blockage if theblockage condition is still satisfied after timer expiry.
 10. Theapparatus of claim 9, wherein the blockage condition is met when eitherthe radio link measurement is above the comparing threshold or the radiolink measurement is above the comparing threshold for a predeterminedtime period.
 11. The apparatus of claim 9, wherein the processor isfurther configured to send a blockage report to a network core inresponse to the comparing of the radio link measurement meeting thethreshold criterion.